You can play the PC and Mac versions of Portal 2 two days before launch in UK shops by buying it from Steam.
The release is the result of an alternate reality game that culminated only a few hours ago. Valve has rewarded those who found all 36 potatoes hidden within the Portal 2 ARG with a free copy of the entire Valve Pack on Steam which includes Portal 2.
UK shops such as GAME still have the first-person puzzler down for release on Thursday 21st April.
Eurogamer's Portal 2 review is live.